A current reference is a circuit used to provide a reference current to a circuit. The circuit uses the reference current as a means of biasing various components within the circuit. For example, current references are used to provide an accurate bias for components such as oscillators, amplifiers, phase locked loops, or other suitable components.
In some approaches, the current reference is formed using bipolar junction transistors (BJTs) to form bandgap references to provide the reference voltage signal. In PNP BJTs the substrate acts as a collector for the BJT rendering the BJT sensitive to majority carrier noise in the substrate. In NPN BJTs the collector is formed as an n-well in a p-type substrate and is susceptible to picking up minority carrier noise from the substrate. Neither NPN BJTs or PNP BJTs allow full isolation from substrate noise.
In some approaches, a temperature independent resistor, such as a silicon chromium resistor, is used in combination with a voltage reference. In some approaches, a proportional to absolute temperature (PTAT) current source is used in combination with a complementary to absolute temperature (CTAT) current source to reduce temperature dependency of a generated current.